ESPECIES

Sex ratio in relation to timing of breeding, and laying sequence in a dimorphic seabird

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Velando, A., Graves, J. & Ortega-Ruano, J. E. Sex ratio in relation to timing of breeding, and laying sequence in a dimorphic seabird. Ibis 144, 9–16 (2002).

When the cost of rearing sons and daughters differs and the subsequent survival and reproductive success of one sex is more dependent than the other, on the amount of parental investment, adult females tend to produce more chicks of the more dependent sex if the females are in good condition themselves. One method of varying the total investment in each sex is through modifying the sex ratio of offspring produced. This study shows that in broods of European Shags Phalacrocorax aristotelis, the sex ratio varied with laying date. Presumably in this species, the lifetime reproductive success of males is more dependent on the level of parental investment. Early breeders are in better condition, the brood sex ratio of early broods was male biased (0.63), while that of late broods was female biased (0.36). The overall difference in sex ratio found between early and late nests could be attributed to manipulation of sex in the first laid egg. In early broods, 77% of the first hatched chicks were male but only 30% of the first hatched chicks in late broods were male. The sex combination of the first two chicks in a brood significantly affected growth as measured by asymptotic mass.

Nest site characteristics, occupation and breeding success in the European Shag

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Velando, A. & Freire, J. Nest site characteristics, occupation and breeding success in the European Shag. Waterbirds 26, 473–483 (2003).

The European Shag (Phalacrocorax aristotelis) breeds in a wide range of nest-sites depending on the locality, such as crevices under fallen rocks, open ground caves and open ledges on craggy cliffs. In this paper the habitat selection of shags breeding in cavities on the coastal slopes of Islas Cíes (Galicia, Northwest Iberian Peninsula) are examined. Shags selected sites with more lateral and overhead cover, with better drainage and with average visibility. In addition, sites where breeding was successful differed from unsuccessful sites. Nest-site characteristics especially affected the hatching success. In this colony, shags showed adaptive responses to site-quality variability. Thus, nest-site quality declined with density and with seasonal occupancy. Shag colonies seem to follow an ideal despotic distribution, where some individuals monopolize high quality sites and prevented other individuals from settling in the good sites. Further studies are required to assess the proximal mechanisms used for nest-site selection in this species.

How general is the central-periphery distribution among seabird colonies? Nest spatial pattern in the European Shag

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Velando, A. & Freire, J. How general is the central-periphery distribution among seabird colonies? Nest spatial pattern in the European Shag. The Condor 103, 544–554 (2001).

La distribución de los nidos en aves coloniales puede ser explicada por dos modelos. El modelo centro-periferia implica que las aves que crían en el centro de una colonia son menos accesibles a los depredadores, poseen una mejor condición y tienen un mayor éxito reproductivo. En cambio, el modelo centro-satélite sugiere que aves de baja calidad construyen sus nidos cerca de parejas de alta calidad para obtener ventajas como un mayor número de cópulas extrapareja por parte de hembras de baja calidad o un mejor sitio de cría o pareja en la siguiente estación de cría. En el presente estudio, nosotros contrastamos estos modelos con la distribución de la calidad de las parejas de Phalacrocorax aristotelis en dos colonias (Portelo y Faro) de las Islas Cíes situadas en Galicia, noroeste de España. Hemos utilizado como indicador de la calidad de la pareja los residuales del éxito reproductor, eliminando el efecto de la calidad del sitio de nido. En la colonia del Portelo se observó una correlación negativa entre la calidad de las parejas a una distancia menor de 4 m; en el Faro, en cambio, no hubo evidencias de una distribución diferente al azar. Además, se encontró una correlación espacial negativa entre los sitios de nido en los que se construyó un nido por primera vez y los sitios que fueron reocupados. En global, estos resultados muestran que la distribución de las colonias del P. aristotelis no corresponde al modelo centro-periferia, sino más bien al modelo centro-satélite o en todo caso, a una distribución al azar.

Intercolony and seasonal differences in the breeding diet of European shags on the Galician coast (NW Spain)

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Velando, A. & Freire, J. Intercolony and seasonal differences in the breeding diet of European shags on the Galician coast (NW Spain). Marine Ecology Progress Series 188, 225–236 (1999).

The seasonal and spatial variations in the dlet of the European shag Phalacrocorax aristotelis were studied during the breeding period, based on the analysis of 202 adults’ pellets (February to June, 1995) and 30 regurgitatons of chicks (April, May and June, 1995 and 1996) taken from 2 colonies located in close proximity to one another ( < l 5 km) on the coast of Galicia (W Spain; Islands of Cies and Ons). The diet of birds from the Cies Islands consisted mainly of sandeels (family Ammodytidae), which make up over 70% of the prey during all months. These fishes went practically unreported in a number of previous studies of fish communities in the region, probably due to the low catchability of trawl nets and the possibility that the habitats of sandeels where shags forage, shallow (<10 to 15 m) sandy bottoms, were not sampled adequately. Seasonal changes were found on the Island of Ons, where in winter (February and March) the diet was based on gobids (family Gobiidae) and sand smelts Atherina presbyter, while In spring the dominant prey were the Ammodytidae (in May and June they made up over 86%). The consumption of sandeels established an increased similarity in diet between the colonies throughout the breeding cycle, and they were the only prey whose abundance was negatively correlated with the diversity of each pellet. This study highlights the high plasticity in prey and feeding habitats (both pelagic and benthic with different types of substrates) used by the European shag. It should be noted, however, that the main prey during chick rearing are sandeels. Differences were found in the mean sizes of the different prey consumed, but the modal size for all of them throughout the season was around 9 to 11 cm in total length. The range of sizes available in the environment is greater than the range chosen by the European shag, which suggests that this bird selects a narrow range of prey sizes.

Coloniabilidad y conservación de aves marinas: el caso del cormorán moñudo

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Velando, A. & Freire, J. Coloniabilidad y conservación de aves marinas: el caso del cormorán moñudo. Etología 7, 55–62 (1999).

En el presente trabajo exponemos cómo los estudios de coloniabilidad pueden ser aplicados a la conservación de aves marinas. Los estudios realizados en las Islas Cíes (NO de España) muestran cómo en las colonias del cormorán moñudo (Phalacrocorax aristotelis) existe una atracción de las parejas de baja calidad y/o jóvenes a criar cerca de las de alta calidad. En la Isla de Ons la dinámica espacial de las colonias señala la importancia de la limitación de los sitios de cría, el contexto social y la emigración dependiente de la distancia en los procesos de reclutamiento. Estos estudios nos permiten diseñar criterios de conservación no exclusivamente numéricos. Así para el cormorán moñudo se recomienda la creación de una serie de enclaves protegidos en cadena. También señalan la importancia de la atracción en la restauración de colonias de aves marinas.

Heterozygosity–fitness correlations in a declining seabird population

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Velando, A., Barros, Á. & Moran, P. Heterozygosity–fitness correlations in a declining seabird population. Molecular ecology 24, 1007–1018 (2015).

Loss of genetic diversity is thought to lead to increased risk of extinction in endangered populations due to decreasing fitness of homozygous individuals. Here, we evaluated the presence of inbreeding depression in a long-lived seabird, the European shag (Phalacrocorax aristotelis), after a severe decline in population size by nearly 70%. During three reproductive seasons, 85 breeders were captured and genotyped at seven microsatellite loci. Nest sites were monitored during the breeding season to estimate reproductive success as the number of chicks surviving to full-size-grown per nest. Captured birds were tagged with a ring with an individual code, and resighting data were collected during 7-year period. We found a strong effect of multilocus heterozygosity on female reproductive performance, and a significant, although weaker, effect on breeder survival. However, our matrix population model suggests that this relatively small effect of genetic diversity on breeder survival may have a profound effect on fitness. This highlights the importance of integrating life history consequences in HFC studies. Importantly, heterozygosity was correlated across loci, suggesting that genomewide effects, rather than single loci, are responsible for the observed HFCs. Overall, the HFCs are a worrying symptom of genetic erosion in this declining population. Many long-lived species are prone to extinction, and future studies should evaluate the magnitude of fitness impact of genetic deterioration on key population parameters, such as survival of breeders.

Population trends and reproductive success of the European shag Phalacrocorax aristotelis on the Iberian Peninsula following the Prestige oil spill.

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Velando, A., Alvarez, D., Mourino, J., Arcos, F. & Barros, A. Population trends and reproductive success of the European shag Phalacrocorax aristotelis on the Iberian Peninsula following the Prestige oil spill. Journal of Ornithology 146, 116–120 (2005).

In 2003, immediately following the Prestige oil spill in Galicia, Spain, we studied the population trends and reproductive performance of European shags (Phalacrocorax aristotelis) at oiled and unoiled colonies. This bird is an important member of the nearshore marine community, breeding in the area affected by the Prestige oil spill. The European shag feeds around the breeding colonies throughout the year, making it a useful indicator of environmental change. Before the oil spill, population trends were similar between oiled and unoiled colonies. Nevertheless, colonies located within the path of the oil suffered greater declines (ca. 10%) compared with pre-spill trends and with population trends at unoiled colonies. In 2003, the breeding success was 50% lower in oiled colonies compared with unoiled colonies. The data available from pre-spill years suggest that the annual reproductive success did not differ among colonies before the impact. European shags breeding at colonies affected by oil showed a negative initial impact from the Prestige oil spill. The reduction in reproductive success at oiled colonies may be due to sublethal effects of oil exposure or low food availability after the oil spill.

The status of the European Shag Phalacrocorax aristotelis population on the Atlantic coast of the Iberian peninsula

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Velando, A., Docampo, F. & Alvarez, D. The status of the European Shag Phalacrocorax aristotelis population on the Atlantic coast of the Iberian peninsula. Atlantic Seabirds (1999).

A regional analysis of the status of the European Shag Phalacrocorax aristotelis population on the Atlantic coasts of the Iberian Peninsula is presented. This is the first census to be made of this population. The total population was estimated to be approximately 2239 pairs in 1990-94. The first counts from Euskadi and Cantabria are presented, indicating a population of 57-67 pairs in Euskadi in 1994 and 36-41 pairs in Cantabria in 1992. The first census in Asturias dates from 1986 with 98-124 pairs, and the population has increased at an annual rate of 6%, reaching 199-250 pairs in 1997. There are records of partial counts made in Galicia since 1976. The population appears to have stabilised on the Cíes and Ons Islands (Rías Baixas, Pontevedra), where it was increasing at 8-9% annually. The total count of 1462 breeding pairs on Cíes and Ons accounts for 66% of the Atlantic Iberian population. As far as is known, the population in Portugal has stabilised, but there has been no census of the southern colonies since 1983. On the island of Berlenga there were 60 pairs in 1990-94, the number of pairs having changed very little since the first count in 1939.

Assessing the effects of the Prestige oil spill on the European shag (Phalacrocorax aristotelis): trace elements and stable isotopes

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Sanpera, C., Valladares, S., Moreno, R., Ruiz, X. & Jover, L. Assessing the effects of the Prestige oil spill on the European shag (Phalacrocorax aristotelis): trace elements and stable isotopes. Science of the total environment 407, 242–249 (2008).

The Prestige oil spill resulted in the mortality of several seabird species on the Atlantic NW coast of Spain. Shag casualties were particularly relevant, since populations are resident in the area the whole year round and because of several features which make them highly vulnerable to environmental hazards. Ecological catastrophes give us the opportunity of collecting samples which, otherwise, would be difficult to obtain. We examine the potential of shag corpses as bioindicators of inorganic pollution and the possible factors of variability, such as biological traits (sex, age) or nutrition status. We determined trace elements (Hg, Se, Cr, Pb, Zn and Cu) and isotopic signatures (15N, 13C) in soft tissues (muscle, liver) and in primary feathers formed at different times (before and after the Prestige) in individuals of known sex and age, collected at the time of the Prestige disaster. These were compared with data from another group of shags trapped accidentally in fishing gear in 2005. Our results did not seem to be affected by sex or age on any of the analysed variables. The higher nitrogen isotopic signatures in  the soft tissues of the Prestige shags may be related to the nutrition stress caused by a poorer body condition,which is also reflected in increasing levels of some metals in the liver.This isotopic enrichment was also observed in newly forming feathers when compared to the old ones. On the other hand, the lower δ15N and Hg values in shag feathers from2005 point to a shift in feeding resources to prey of lower trophic levels.We found that feather features (being an inert tissue and having a conservative composition), if combined with careful dating and chemical analysis, offer a very useful tool to evaluate temporal and spatial changes in seabird ecology in relation to pollution events.

Influencia de la colonia de gaviota patiamarilla (Larus cachinnans Pallas) sobre el contenido de nutrientes (amonio y fósforo) en los suelos de los acantilados del Parque Natural de las Islas Cíes (SO de Galicia, NO de España).

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Otero Pérez, X. L. Influencia de la colonia de gaviota patiamarilla (Larus cachinnans Pallas) sobre el contenido de nutrientes (amonio y fósforo) en los suelos de los acantilados del Parque Natural de las Islas Cíes (SO de Galicia, NO de España). Thalassas 14, 57–62 (1998).

Los análisis realizados pusieron de manifiesto la presencia de concentraciones importantes de amonio (32.50 mg g-1) y de fósforo (16.58 mg g-1) en excrementos frescos de la gaviota patiamarilla (Larus cachinanns). Los resultados obtenidos para los suelos reflejaron un claro enriquecimiento en amonio cambiable y fósforo asimilable en los suelos de los acantilados donde se establece la colonia de esta especie. Las concentraciones de amonio presentaron diferencias entre las áreas de cría y la zona control (sin gaviotas), pero no entre las zonas de cría con densidades diferentes. Sin embargo, todas las áreas mostraron diferencias significativas entre ellas para el fósforo asimilable. Estos resultados parecen estar de acuerdo con el ciclo biogeoquímico de cada uno de estos dos nutrientes. El amonio puede ser oxidado pasando a la forma NO3- y este puede ser lavado fácilmente del suelo ya que apenas se encuentra absorbido por los coloides del suelo. Por el contrario los fosfatos pueden ser absobidos de manera específica por formas activas de Al y/o Fe o formando precipitados de Ca, Al, NH4+ y Fe3+ de baja solubilidad. Estos procesos favorecen su permanencia y acumulación en el suelo.